In general, in an air-tight, ill-ventilated room such as an office room or meeting room, the presence of a large number of people in it increases the amounts of air pollutants such as carbon dioxide—which the people breathe out—cigarette smoke, and dust. This reduces the quantity of negative ions—which have the effect of relaxing humans—present in the air. In particular, the presence of cigarette smoke may reduce the quantity of negative ions to about ½ to ⅕ of their normal quantity. To cope with this, various ion generating apparatuses that are designed to replenish the air with negative ions have conventionally been commercially available.
However, conventional ion generating apparatuses exploiting electric discharge are typically of the type that generates negative ions by the use of a high negative direct-current voltage, and are aimed at appealing to consumers with a relaxing effect. Accordingly, such ion generating apparatuses can simply replenish the air with negative ions, but cannot actively remove airborne bacteria and the like floating in the air.
Here are the results of our searching the past patent publications for examples of other types of ion generating apparatuses.
Japanese Patent Application Laid-Open No. H4-90428 (hereinafter referred to as Patent Publication 1) describes an ion generator wherein a high alternating-current voltage is applied to a discharge wire or a discharge plate having an acute-angled corner to generate negative ions alone or both negative and positive ions. This publication, however, only makes mention of a high alternating-current voltage unit as to the method or means of generating ions. Here, the assumed area of application is air conditioners, and the asserted effects are comfort and relaxation to humans.
Japanese Patent Application Laid-Open No. H8-217412 (hereinafter referred to as Patent Publication 2) describes a corona discharger that has a pair of electrodes, namely a discharge electrode and an induction electrode, arranged so as to sandwich an insulating member and that is provided with a high-voltage power supply for feeding a high alternating-current voltage between those electrodes. This publication describes the high-voltage power supply as having a diode connected between the electrodes so that, according to the direction in which the diode points, either a negative potential or a positive potential is chosen as the supplied voltage. However, this publication makes no mention of how such switching is achieved. Here, the assumed area of application is corona discharge equipment such as ozone generating apparatuses, charging apparatuses, and ion generating apparatuses. The asserted effect is generation of ions.
Japanese Patent Application Laid-Open No. H3-230499 (hereinafter referred to as Patent Publication 3) describes an ion generating apparatus wherein a large number of pairs of electrodes—each pair consisting of a needle-shaped discharge electrode and an conductive grounding grid or ring—arranged two-dimensionally across the stream of purified air, and wherein a negatively biased high sinusoidal alternating-current voltage is applied to some of the discharge electrodes and a positively biased high sinusoidal alternating-current voltage is applied to some other of the discharge electrodes so that, of the plurality of pairs of electrodes, some release positive ions and some other release negative ions. This ion generating apparatus includes a means for controlling the bias voltage, and this permits adjustment of the quantities of positive and negative ions. The assumed area of application is charge neutralizing equipment for clean rooms, and the asserted effect is neutralization of electric charges.
Japanese Patent Application Laid-Open No. H9-610 (hereinafter referred to as Patent Publication 4) describes a dust collecting apparatus wherein the voltages applied to electrodes at which to cause positive and negative electric discharge are variable. The electrodes are an ionizing wire and a dust collecting plate, which are designed to charge dust and thereby collect it in on the dust collecting plate. The assumed area of application is electric dust collecting apparatuses for air conditioning equipment, and the asserted effect is sterilization of the interior of such apparatuses by the action of the ozone generated by electric discharge.
Ion generating electrodes exploiting electric discharge divide roughly into two types. One type is, as described in Patent Publications 1, 3, and 4, a metal wire, a metal plate having an acute-angled corner, or a needle combined with, as an opposite electrode, the earth or a metal plate or a grid kept at the grounded potential, with air serving as an insulating member. The other type is, as described in Patent Publication 2, Japanese Patent Application Laid-Open No. 2003-47651 (hereinafter referred to as Patent Publication 5), and Japanese Patent Application Laid-Open No. 2002-319472 (hereinafter referred to as Patent Publication 6)—of which the latter two will be described later—a combination of a discharge electrode and an induction electrode formed with a solid dielectric member sandwiched in between. The former is characterized in that the use of air as an insulating member permits the electrodes to be kept farther away from each other than in the latter and thus requires a higher voltage to cause electric discharge. By contrast, the latter is characterized in that the use of an insulating member having a high insulation resistance and a high dielectric constant permits the distance between the electrodes to be made smaller (narrower) and thus requires a lower application voltage than in the former.
There have conventionally been made inventions relating to ion generating apparatuses (for example, see Patent Publications 5 and 6) that exploit the effects produced by releasing ions of opposite polarities, i.e., positive and negative ions. These ion generating apparatuses generate and release into the air approximately equal quantities of H+(H2O)m as positive ions and O2−(H2O)n as negative ions (where m and n are natural numbers) so that those ions surround airborne mold spores and viruses floating in the air and deactivate them by the action of a free radical, namely hydroxyl radical (.OH), generated as a result.
These inventions have already been put into practical use by the applicant of the present application. The actual products are ion generating apparatuses composed of a ceramic dielectric member, a discharge electrode arranged outside the dielectric member, and an induction electrode arranged inside the dielectric member, and air purifiers and air conditioners incorporating such ion generating apparatuses.
Negative ions are believed to produce the following effects. In a space in a household where an excessive quantity of positive ions are present due to electric appliances or for other causes, releasing a large quantity of negative ions helps to restore a state in which well-balanced quantities of positive and negative ions are present as in a wild forest, and to obtain a relaxing effect. Patent Publication 1 makes mention of such a relaxation effect.